The present invention relates to a motor vehicle comprising a frame chassis including two longitudinal beams and at least a first and second cross members between said two longitudinal beams, and a battery box arranged at the rear end of the vehicle between said beams with mounting means.
A battery box support assembly of such kind is known from EP 1334881 A2.
In particular in some semi-tractor variants, the battery box is positioned in the rear end of the truck, i.e. the end of the frame, in order to ensure a good weight distribution in the truck and because the space in the centre of the vehicle is limited. This rear end battery position is also advantageous as the batteries are well protected in case of a collision as they are positioned inside the chassis frame at the rear of the truck. However, this rear end battery position also displays some drawbacks. The movement of the frame is greater in the rear of the truck than in the centre of the truck. This applies both to vibrations caused by an uneven ground and to sideways movements caused by turning. Vibrations caused by an uneven ground will introduce longitudinal and horizontal movements.
The battery box known from EP 1334881 A2 is resiliently mounted to the longitudinal beams of the vehicle. Although the batteries may be protected from these longitudinal and horizontal movements by the known system, the battery box support system does not absorb the sideways movements due to vehicle turning. One reason is that the resilient mounting means are adapted for longitudinal and horizontal movements. Another reason is that the truck frame is less stiff when it comes to side forces. Since the batteries are heavy. The frame will thus flex somewhat, particularly in the rear end of the truck.
The movements caused by turning will be much greater than the movements caused by vibrations since a small turning action with the steering wheel will cause a large movement at the rear of the truck. To extend the life of the batteries, it is advantageous to limit the movement of the batteries as much as possible.
Moreover, the battery support system of EP 1 334 881 may be difficult to arrange due to other parts that must be mounted to the longitudinal chassis frame or accommodated inside the cavity of the chassis frame beams.
On this background, it is desirable to provide a vehicle with a rear end mounted battery box without the above-identified drawbacks.
According to an aspect of the present invention, a motor vehicle of the initially mentioned kind is provided, wherein the mounting means of the battery box comprises front mounting means connecting the front side of the battery box to the first adjacent cross member and rear mounting means connecting the rear side opposing said front side of the battery box to the second adjacent cross member.
By mounting and suspending the battery box from the cross members of the chassis frame, the mounting brackets do not collide with other components that must be accommodated in or mounted on the longitudinal chassis beams. Moreover, the battery support system according to an aspect of the invention provides an advantage in terms of space. A low battery position may be advantageous with respect to weight distribution in the vehicle and contribute to a low centre of gravity of the vehicle. A low battery installation is possible by an aspect of the invention since the mounting brackets can be placed on the cross members relatively unrestricted, or the cross members may be specially designed to provide for a low position of the battery box. By an aspect of the invention it is possible to tailor the position of the cross members and the vertical position of the battery box.
A further advantage is that the cross members are stiffer for side forces caused by sideway movements, e.g. caused by turning. By an aspect of the invention, it is realised that the mounting brackets are typically less dampening with respect to compression and stretching than to bending. Consequently, by an aspect of the invention a higher sideways stiffness is achieved.
Advantageously, the mounting means comprises rubber suspension brackets providing an elastomeric connection between the battery box and the cross members of the vehicle frame. However, it is realised that other types of brackets or vibration or movement absorbing mounting means may be used for connecting the battery box to the vehicle frame.
The front and rear mounting means may be different in respect to size and/or resilient characteristics. This may be advantageous since the movements at the front and the rear of the battery box differs in amplitude. When the front or the rear mounting means is a single mounting bracket, this may comprise a hinge.
The mounting means may preferably comprise four brackets for mounting the battery box. However, it is realised by an aspect of the invention that the battery box may be mounted with three mounting brackets, where either the front mounting means comprise at least one bracket and the rear mounting means comprises at least two brackets or where the front mounting means comprise at least two brackets and the rear mounting means comprises at least one bracket. A three point mounting of the battery box in the vehicle frame may be advantageous e.g. if the space is limited due to other components that must be fitted to the frame, if the weight distribution in the battery box is uneven, or if a special vibration dampening characteristics is required.
Preferably, the mounting means provide a symmetrical mounting of the battery box along the longitudinal axis of the vehicle. However, an asymmetric mounting is made possible by e.g. a three point mounting.